Annealing Brass Cartridge Casings with a short (2- layer X 3 Turn) coil:I just put this video on youtube last night:

/>Many ammunition "reloader" guys ask about this, so I thought I'd try a coil design that might work. (I am not a relaoder guy), I see that some already do use these small induction heaters to do this task, but I am not sure they are running their systems in a sustainable way.So my focus is to make sure that Mosfet gates turn on rapidly by using coil designs that keep the oscillation frequency to acceptable (upper) limits.

Peterspaco:I hope to cast bigger things so even a 3kg crucible is too small. I made a whole sword with aluminium when I ran my propane mini kiln!

badpeter, keep up the good work, very curious to know how much copper you will be able to melt. I am also interested in melting larger quantities (1-5 lbs esp.) knifes, swords, parts, etc. but have not yet purchased this 2500W unit because AFAIK no one else has reported that they can melt more than 500 grams, at lest repeatedly. So probably this design just does not have enough power to melt larger quantities (maybe it can melt a pound or two max if tweaked properly?) Peterspaco has the best tests and has confirmed repeatable 500 kilogram melts with excellent results. I'm hoping that someone shows what the practical limit of the melt size is, especially for copper casting alloys. Obviously at some weight, it will not melt a given quantity no matter how long you run it, and if takes too long (say 1 hour?) then the metal will probably pick up too much oxygen causing porisity, etc. Will it melt 1,2, 3 lbs. in 15 minutes, 30 min, 60, never... ? Peterspaco total power output is only approx 1600 watts when melting copper so we are already close to maxing out the power. There is some headroom there - approx 700W that is still available - however this power is not being used because this unit can not output anymore amps to the crucible/copper load. Possibly, if the crucible was a heavier gauge steal then it might utilize unit's full 2500 Watts, however, I don't think that you would ever want to melt copper in steal because it would absorb way too much iron causing embrittlement, poor properties. I know very little about induction heating so tweaking the board to run hotter (larger caps,etc.) is beyond me. For all I know it is not even possible or if so, prohibitively expensive. We do have other alternatives. Larger, though much more expensive induction furnace. I did contact a regular industrial supplier of induction furnaces here in the states and was quoted $5000 for their smallest unit that can melt 4-6 lbs of copper in 5 minutes). When I said that was way out of my budget he basically hung up on me. Though he did say theirs are built way better. A custom sized DIY propane/gas furnace will easily melt 5-30 pounds. Resistance furnace is another option. Those 2-3 kilo gold/silver melting units that sell for about $300 - however I wonder if they are also under-powered for melting more than even a kilo or two of copper? The thing that draws me to both electric induction and electric resistance melting is the noise factor - not bothering my nice neighbors. Another possibility is some type of custom DIY arc furnace. An arc type furnace may actually be the most efficient and quickest method for my size melts, though again the commercial units are prohibitive and there is even less DIY info on them. Eventually, I will decide on probably one of these three electrical methods. With limited electronic knowledge and resources the decision for me will boil down to good proven info from DIY sources and of course economics. Opinions on the best electric method for small size melts of 1 to 5 lb size melts?

I just tried melting some more copper with the 2500 watt unit.It went well despite my making a newby mistake by putting to much cold metal into the molten copper in the crucible.The video is here:

/>Interestingly, the current dropped more than in previous melts as the copper first melted. I think I have some ideas about that, which will require further testing, one of these days, But, even at 24 gross amps, (18 amps net) and 48 volts or (864 watts), the full crucible sure did melt well.

Hightemp: Well, the way I see it, power output will determine how quickly you heat things up and WHERE the thermal equilibrium is reached - aka power IN starts being equal power OUT. It is also determined by losses. Even if energy is pumped in at a slower rate, but you somehow can magically improve insulation, you will reach equilibrium at higher temperatures. The other thing to note is, exponentially more energy is required to raise something to a degree at higher temperatures than at lower temperatures (relative to outside temp that is). That fact was especially evident with my other-other pottery kiln which lights up an LED when SSR is on so it is easy to see the difference.

You can reliably melt about 3 kg s of copper with about 800 W. I will be doing further tests + casting via lost PLA method soon ish, will have real numbers. It is funny how i started thinking like a scrapper a bit - always checking if there is some copper laying around somewhere haha. peterspaco: I nearly doubled the coil so it covers full crucible. Power stayed nearly the same, even decreased a bit. Frequency has halved. I think the only way to increase output is to change diameter that can't be done currently with my setup. To kind of summarize it (correct me if i am wrong) but MORE power is drawn if we have:Lesser coil diameterMore material inside the working volumeHigher frequencyLess turns in the coil

I just tried melting some more copper with the 2500 watt unit.It went well despite my making a newby mistake by putting to much cold metal into the molten copper in the crucible.The video is here:

/>Interestingly, the current dropped more than in previous melts as the copper first melted. I think I have some ideas about that, which will require further testing, one of these days, But, even at 24 gross amps, (18 amps net) and 48 volts or (864 watts), the full crucible sure did melt well.

Congrats - Job Well Done - Thank you so much, you are the best !! That was a significant amperage drop compared to the last melt, approximately 30% net amps drop, at least towards the end (18 net vs 26 net amps). The only difference is the extra charge, I think (9 ounces vs 18 ounces)? It is confusing why these units can not maintain amperage throughout the melt. I'd almost think that with the crucible filling with metal that the amperage would if anything go up, but then again, induction heating is mostly Greek to me. badpeter is going to be doing some similar size melts and casting in molds, so his tests may confirm this, if they have not already? Great stuff guys - love it! Foundry fumes can be nasty so if you don't already have some kind of exhaust system, you may want to add one. I use a simple box fan cranked on high with same size heppa filter attached to the back.

Correction: Not sure, but I think brass shot would be a better "thinner" than pure zinc since zinc would instantly vaporize at copper melt temps. Brass shot would give off a lot of zinc fumes as well but might have a better chance mixing if "dunked" under the melt. Aluminum bronze is being used for swords and such cause it is one of the strongest copper alloys even without high tech heat treatment. But the ratios need to be more precise and may be more difficult to cast because of shrinkage.

Thanks for sharing your results. This is my version for annealing brass:

This is off topic, but to whom it may concern: I'm having difficulty with this site. I get a lot of 403 errors when clicking on links. I can get 2-3 page loads before I get blocked. I can still load pages through a proxy, but then I can't post. To post I have to remember what I wanted to post from the previous day and do that first, after a couple attempts because "Your session timed out while posting. Please try to re-submit your message." For me, this really detracts from the experience...

How far down the casing does the anneal go? ( I have heard that you don't want to go any farther than the just the neck).I'd think you'd want to quench in water, but I guess many folks do as you do.

How about some numbers:-System power capability-Net Current to the work-Temperature (I see things glow a LOT, but with white balance problems being what they are, I can't tell.) What temp ARE you aiming for?-Frequency

^wow so much activity here!Well, I managed to melt my first copper! so yay...I rebuilt the PS with a powerful fan underneath, using the original box. It looks very neat.But most importantly, insulation does miracles.

The data is the following: 845 g of copper melt in a graphite crucible (so-called "3kg-crucible" on ebay)in about an hour with an output of just under 1kW.

the question is, how do I draw more power?

Badpeter, any luck on getting more power? Wonder what would happen if you added another one of the donut things and put in parallel? The extra 500 or so watts may greatly reduce your melt times and the metal may be cleaner - less time to pick up oxygen, dross, etc. Petespaco gets between 32 and 38 amps when melting about 9 ounces, however on the last larger 1.2 lb copper melt test the amp output dropped all the way to 26 amps or 1250 watts, after all the metal was added. I have not yet decided on a PS. Possibly a MOT rated at 1250 Watts or more. At 50 volts that is about 25 amps. Problem is getting 60 turns when manually rewinding magnetic wire that is heavy enough to handle say 32 amps all day long. Petespaco amazingly got about 41 turns producing 31 volts on a small test MOT here on YouTube.

Potential problems deal mostly with rewinding - choosing correct wire gauge (ie single a 14 gauge wrap or ganging multiple gauges in parallel, say three 18 gauges together, also scaring the wire while wrapping and expense of magnetic wire. Curious, how much did you pay for those donuts? Anyhow, hope that you eventually show us some more of your bigger melts and some cool castings.

NOTE: My MOT ideas are based on assumption the 2500 ZVS works best at 48 voilts.

Hightemp: I think the only way to get more power is lesser-diameter coil and more material/graphite in that diameter. I don't think I can alter my current setup much anymore. My donut is using two secondaries in paralel to help with distributing high current over twice the wire as well as for cooling reasons (more turns take up more area of the donut). Adding things in paralel will do nothing. To draw more power - something has to consume it (aka work piece). It cannot be forced.I have made some ingot molds outta plaster+sand (50/50) as well as a mold for a british ww2 thin dagger off a 3D printed piece from Thingiverse. I also printed a sphinx figurine to test out lost PLA method. When i did that, someone suggested purchasing a roll of water soluble PVA filament and just use that to print with! that be so much simpler. Re power supply, I see that ebay has so much more to offer now! I would've never gone with the donut if these options were available for a comparable price for high power regulated psu (around 90$). the diy donut transformer journey was a long one and I do not recommend it.

Re MOT - seeing how transformers drop a lot in voltage when connected to load, I overvolted mine when load free such that when idle zvs is connected voltage drops back to around 55 volts. (overvolt was on the order of 15 V or so - quite a bit). This killed the fans by the way, connect them to external supply if you go that way).

I am amazed that you melted almost 2 pounds (845 grams) on less than 1000 watts. Did you have much metal loss, and dross on the 1 hour melt? I wonder how petespaco's power would drop if he tried 2 pounds on a bigger coil/crucible - maybe similar to yours - or about 1 kilowatt power when fully melted? What is inside diameter of your coil and crucible's approximate area - or is 6 kilogram capacity for copper or gold? Thanks for the fan tip on overvoltage for mots.

I did some simple two part plaster casting years ago using metal casting plaster, basically what you are using, sand and plaster. Make sure to dry them completely, regular kitchen oven works fine. Pouring when molds are hot 450 degrees helps with mold filling. Did not try any lost wax casting but the water soluble patterns sound very interesting. If you can dissolve/drain pattern within mold without loosing pattern detail and without contaminating mold so that high temp burnout is unnecessary then it would simplify the process considerably. I'd be very interested to know how that turns out for you. Have you poured the 3-D figurine, or knife molds yet? Please keep me posted !!

There wasnt much dross, copper was clean, mostly from av cables. Coil has a diam of 12 cm and something like 16 turns.Here is my youtube channel where I melt some aluminium with my other diy propane kiln (sword and ingots in another one). When I finally get to make an induction video will post that on there too.

/>Also, on unrelated note, the epic power plant tour vid may be of interest to high voltage enthusiasts... but thats a different story...

There wasnt much dross, copper was clean, mostly from av cables. Coil has a diam of 12 cm and something like 16 turns.Here is my youtube channel where I melt some aluminium with my other diy propane kiln (sword and ingots in another one). When I finally get to make an induction video will post that on there too.

/>Also, on unrelated note, the epic power plant tour vid may be of interest to high voltage enthusiasts... but thats a different story...

Thanks for info and for sharing your video. Sword looks beautiful -congratulations! I encourage you to finish and put on your mantel. Possibly to eliminate air holes you need more metal to melt to allow for a riser and/or a gate, not sure though as I have never casted anything that big? Correction on prior post -you are using a sand type mold, different than the "plaster of paris" type mold I used where you mix equal parts of water to very fine sand/plaster, pour on pattern then let it set so it is rock hard. I know little about sand casting so don't have any other tips but there are many videos on youtube about sand casting. Luckygen1001 is one of the better ones to check out. He does lots of aluminum, bronze, zinc and cast iron with fantastic results.

Wow, you are using huge coils -almost 5 inches and still getting descent power. That is very interesting as I still have an old salamander graphite crucible about that size -may have to get it out of the moth balls. If you do 3-D printing those could go hand in hand with these induction melters, giving you an unlimited source of intricate patterns. Most of the patterns I made were machined from wood using basic woodworking tools (drill press, router, etc. - the old fashion way).

I've been doing more with work coil design lately. I've just published a somewhat lengthy (sorry about that!) youtube video showing me laboriously producing a 2 Layer 3 Turn coil. Its part of my attempt to heat brass cartridge cases faster, while keeping the ZVS heater board safe and able to run continuously without failure.Anyway, to make it easier to follow those "exploits", I also just put up a webpage dedicated to the work coils themselves.It will be updated regularly for the next few months at least.It's at:http://www.spaco.org/Blacksmithing/ZVSInductionHeater/WorkCoilsForZVSInductionHeater.htmAny pertinent coil-related videos will be (and already are) linked to on that page.

It looks like most of those guys are also using the cheap chineze boards too. There is not a lot of electronics expertise over there, but they've got things working through trial and error and people sharing their results.

With a better gate control I've been able to run 400kHz without problems. This works well with small, thin cases in small coils. The idea is to quickly heat the neck of the case without heating the head. A small coil allows you to do this, otherwise you just heat the whole case and ruin it. The neck acts like a gasket, so you want it soft. The head has to hold the pressure, so you want it hard. If you soften the head it becomes dangerous because it can "KB" and vent gas and metal particles towards the operator.

These guys have a commercial induction annealer and a lot of technical info published on their web site on brass hardness, etc. if you want to get into the details:

Yes, I have been to both those sites. I am certainly not planning to re-invent the wheel, just to understand these particular ZVS units better.

Re:

Quote

With a better gate control I've been able to run 400kHz without problems. This works well with small, thin cases in small coils.

Believe me, I appreciate the "better gate control" comment.

I have read that the Mosfets we are using are good to at least 1 MegaHz. So it's the design of the gate ckt in these induction heaters that's the problem.And I am not about to monkey around with them.

What voltages and currents can you handle at 400kHz?How much net current or power is going into the casings when you anneal them.You said "small thin cases". is 7mm small? What is "big"?Can you comment on work coil sizes that you use?

As we all know, it is said that higher frequencies work better for transferring power to nonferrous materials. But, really, how big a difference DOES it make? For me, I think these heaters could go up to about 115 kHz or 125 kHz or so which could be about a 25% increase from to ~90 kHz where I am running the 1000 watt unit right now. But is it worth it?

however on the last larger 1.2 lb copper melt test the amp output dropped all the way to 26 amps or 1250 watts, after all the metal was added.

Should read:however on the last larger 1.2 lb copper melt test the amp output dropped all the way to 18 amps NET, or about 864 watts into the work, AT THE MOMENT THAT THE COPPER MELTED .

Thanks for correcting/clarifying. Can you or anyone else explain why the measured amps and power dropped so much from start to finish when melting copper, especially since there is no iron involved? Seams like the more copper we melt the less power these heaters put out? Also, can a large amount of copper, say 2 pounds in a crucible, somehow be arranged to get the full 2500 watt rated watt output using these 2500 ZVS heaters and still have enough power to melt a kilo of copper?

My latest copper melting test video will be up on youtube in about one hour after this message appears.Hopefully it suggests that there may be a way to get more copper melted in a reasonable amount of time

Just kidding, but this paper has a lot of useful information, especially after most of the mandatory academic math is over with, at about Figure 4.

The main take-away that I got is that getting that taller crucible that you mentioned (and, somehow insulating it with a THIN material) and making a work coil with enough turns to encircle it, might really help to transfer more power. This should lower the frequency, which should increase penetration depth, if I got it right.

Again, a caution: If you do this, you really need to be careful not to overtax the system the first time you try it out. Insert the crucible slowly into the work coil.